1. Field of the Invention
The present invention relates to a magenta toner containing a resin for a toner, and a colorant, and a developer and an image forming apparatus using the magenta toner.
2. Description of the Related Art
On the recent market, there have been requirements for downsizing of particle diameters of toners for increasing image quality of images, and for low temperature fixing ability of toners for energy saving. In particular, for energy saving, it is desirable to make an amount of power the lowest possible that is required for a waiting time from when an image forming apparatus is set up to be usable to when image forming is possible (i.e., a warm-up time of an apparatus) and there has been strong demand for shortening the waiting time. Toners obtained by a generally used knead-pulverizing method, however, have been becoming close to the technical limitation for downsizing of their particle diameters, involving various problems such as their amorphous shapes, broad particle size distributions, and high fixing energy required. Particularly in fixing, kneaded-pulverized toner particles produced by a pulverization method crack at the interface with a release agent during pulverization, so that the release agent is present more on their surfaces and easily exhibits its releasing effects. On the other hand, the release agent easily adheres to a carrier or a photoconductor and also to a blade, and such toner particles have not been satisfactory in performances.
In order to overcome the problems with the above knead-pulverizing method, there have been proposed methods for producing a toner based on the polymerization method. This polymerization method enables the toner to be easily downsized in particle diameters, to have a sharper particle size distribution than toner produced by the pulverization method, and to enclose a release agent therein. For example, Japanese Patent Application Laid-Open (JP-A) Nos. 63-282752 and 06-250439 propose methods for producing toner by the emulsion polymerization aggregation method. Also, JP-A Nos. 2000-275907 and 2001-305797 propose techniques that overcome the problems associated with use of a surfactant in the emulsion polymerization aggregation method. Furthermore, JP-A No. 11-133665 proposes a dry toner having a working sphericity of 0.90 to 1.00 using an elongation reaction product of urethane-modified polyester as a toner binder, in order to improve toners in flowability, low temperature fixing ability, and hot offset resistance. Moreover, JP-A Nos. 2002-287400 and 2002-351143 propose a dry toner excellent in all of powder flowability, transferability, heat resistant storage stability, low temperature fixing ability, hot offset resistance when it is formed into a toner having a small particle diameter. Any of these production methods of toner includes a polymerizing step of performing polyaddition reaction between an isocyanate group-containing polyester prepolymer and an amine in an organic solvent and an aqueous medium; and a step of removing the organic solvent by heating etc. In particular, JP-A No. 2005-77776 describes the method of removal of the organic solvent in detail.
These conventional polymerization toners, however, are produced in water, and thus are attached with, for example, soap, particles, and aqueous polymers during the production of toner particles, which makes the resultant toner poor in melting property, adhesion property between toner particles, adhesion property of toner particles on paper upon fixing, so that it is not possible to achieve favorable color properties on paper.
Meanwhile, JP-A No. 2006-267741 discloses a toner containing a naphthol pigment and a quinacridone pigment having specific X-ray diffraction patterns. These pigments, however, use a crystalline substance having a narrow half value width and high crystallinity, and the crystals are hard and large. That is why they are difficult to disperse in the toner to make it impossible to show appropriate density and hue. In addition, pigments to be used in magenta toners have properties of easily localizing at the toner surface, and there has been a problem that they inhibit thermal conduction to toner upon fixing.